JPH0576791B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the construction and use of infrared detectors, particularly photoconductive detectors.

Conventional infrared detectors formed from cadmium mercury telluride (CMT) alloy materials, both simple two-contact photoconductors and single p-n homojunction photodiodes, are well known. In recent research and development, the delay integration function (time−
delay-integration functions) have been attracting attention. For example, in GB 1488258 the detector is strip-shaped and the degree of drift of the photocarrier is adapted to the speed of the scanned image.

A major problem with conventional photoconductors, especially those used in non-scanning "staring" applications, is the presence of a standing DC output (dark current) even when no input flux is present. . Due to the low impedance of conventional long-wavelength intrinsic photoconductors, the standing current is typically a few milliamps, corresponding to a bias of several volts. As a comparative example,
The background flux signal is a few millivolts and the required optical signal is a few microvolts. This dark current is caused by capacitive output coupling.
It is extremely difficult to deduct properly on a steady-state basis, except in the case of scanning systems that can use a coupling.

Photovoltaic detectors, such as photodiodes, do not require bias, do not consume much power,
It has the advantage of no dark current. Junction diode detectors, however, are difficult to manufacture and require large amounts of rare and scarce p-type CMT.
This type of detector also has stability issues during long-term operation as well as the high temperature storage conditions commonly found in military environments.

It is an object of the present invention to provide a high impedance long wavelength intrinsic photoconductive detector. This is because the problem of dark current is minimized if the impedance is high.

According to the invention, the aforementioned object is to provide an n-type semiconductor emitter region of a material sensitive to infrared radiation, a collector region, an emitter contact and a collector contact in contact with the emitter region and the collector region, respectively. a photoconductive infrared detector comprising: a barrier region connecting the emitter region and the collector region; the barrier region comprising a p-type semiconductor material; It has a valence band that is almost common to the valence band, has a wider band gap than the emitter material, and provides a heterojunction conduction band discontinuity to the emitter region, which affects the electron flow between the emitter region and the collector region. This is achieved by means of a photoconductive infrared detector which is characterized in that it is regulated in such a way that the hole flow is substantially unimpeded, although it is a barrier.

The detector exhibits a high impedance because the barrier region prevents the flow of majority carriers from the emitter. However, if illuminated and properly biased, minority carriers will freely pass through this barrier region and a photocurrent will be generated, causing the detector to function as a photoconductor.

The emitter material and the barrier material are preferably ternary alloys of the same chemical species, for example cadmium mercury telluride, or indium gallium arsenide, or gallium aluminum arsenide, n-type/n-type, n-type/
A combination such as p-type or p-type/n-type is preferable. However, the barrier material may be a composition of different species as long as the emitter material and the barrier material have the same or nearly the same valence band. The barrier material may be a binary alloy or compound having a common anion with the ternary alloy, such as cadmium mercury telluride and cadmium telluride, gallium aluminum arsenide and gallium arsenide, or indium gallium arsenide. and indium arsenide.

The collector region may be formed of the same majority carrier type material as the emitter material and with a valence band limit at a level common to, or at least close to, that of the barrier material. Alternatively, a high work function metal of the majority carrier type or a heavily doped semiconductor material of the same type as the emitter material may be used. In the case of metallic material, the collector region is constituted by the collector contact itself.

One form of such a detector is a planar structure in which the emitter, barrier, and collector regions are comprised of layers of n-type, p-type, and n-type material, respectively. In this structure, the emitter region and collector region are the same,
Therefore, the band gap can be made of materials with the same characteristics. This type of detector exhibits non-linear operating characteristics in the illuminated condition and therefore cannot be used with an AC bias source or modulated
It may be included in a circuit with an AC bias source. In this case, it is preferable to arrange an integrator, harmonic filter, or demodulator following the collector. In a modified structure of this type of detector, the emitter material and the collector material are the same majority carrier type material;
One material has a composition suitable for the detection of infrared radiation with a wavelength in the band of 3 to 5 μm, and the other has a composition suitable for the detection of infrared radiation with a wavelength in the band of 8 to 14 μm. The detector is therefore responsive to one band at a time, and this responsivity depends on the bias direction. A detector of this type may therefore be implemented in a circuit with a DC bias, ie a bias source that can be switched from one direction to the other to select a waveband. Alternatively, a circuit with an AC bias source and a phase sense amplifier or gate amplifier connected to the collector may be used. Separately gated circuits generate two channel outputs with data from the individual bands of each channel.

A variant of the detector is a structure that is still planar, but has two layers of different multi-carrier type materials. One layer consists of a material with an extremely wide bandgap,
The other is formed to define the emitter and collector regions of the detector.

Another variation of the detector is one in which the emitter region is comprised of an elongated piece of material, and the barrier and collector regions are arranged to form a readout structure for this piece of material. Such a detector may be placed on the focal plane of the scanning optical system and biased so that the photocarriers generated within the piece of material move at a rate compatible with the scanning speed. In this way, the signal can be integrated on the spot.

The present invention will be described in detail below using preferred embodiments shown in the drawings.

The detection device 1 as a photoconductive infrared detector shown in FIG. 1 has two ohmic contacts 3 and 5.
These contacts are arranged one on each side of a three-layer structure 7 made of cadmium mercury telluride (CMT) material. The first of the three-layer structure 7
Layer 9 consists of n-type cadmium mercury telluride formed from slices cut from a high quality single crystal, and the two upper layers 11 and 13 consist of p-type and n-type cadmium mercury telluride material, respectively. . The p-type layer 11 as barrier region and the n-type layer 13 as emitter region are formed by sputtering or epitaxial techniques [vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), molecular beam epitaxy (MBE) or chemical vapor deposition. (CVD)].

n-type layers 9 and 13 as outer collector regions
is made of a cadmium mercury telluride material (Cd _X Hg _1-X Te: x=0.20).
The donor concentrations of these layers 9 and 13 are both 5
It is on the order of ×10 ¹⁴ cm ^-3 . At operating temperatures of about 80°K (such as with liquid nitrogen cooling), the intrinsic carrier concentration is typically 2.5×10 ¹³ cm ⁻³ and the minority carrier (hole) concentration is 1.2×10 ¹² cm ⁻³ . n-type layer 13
The thickness is thin (≦10 μm) as in the case of a photodetector with a shallow junction. The n-type layer 13, the surface of which is illuminated by focused infrared radiation during operation, has a wide bandgap with contacts 3 that minimize the generation-recombination of minority carriers at the surface of the n-type layer 13. The contact 3 has a composite structure, consisting of a metal edge or metal ring on a thin layer 15 of strongly doped n-type CMT with a somewhat wide band gap (e.g. x > 0.20, 10 μm thickness for n±-type CMT). It is constructed by forming a single ohmic contact 17 having a shape.

The intermediate or p-type layer 11 consists of cadmium mercury telluride with a very wide bandgap of up to 0.5 eV (in other words, this layer is made of a cadmium-reinforced material: x~0.45). The p-type layer 11 has n-type layers 9 and 13 above the valence band (VB).
is a doped p-type layer with the same or nearly the same Fermi level (FL) as . Because the density of states in the valence band is similar (the effective hole mass is 0.55 regardless of composition), the hole concentration is fairly constant throughout the device. The interface between the n-type layer 13 and the p-type layer 11 is a pn junction without a depletion region, ie, without a space charge layer at zero bias. The thickness of the p-type layer 11 is 3 to 10 μm, taking into account the balance between tunneling, conductivity, trapping, and depletion state in the bias state.

In this structure (FIG. 1) the flow of electron current is blocked by an energy barrier (FIG. 2). This is due to the discontinuity of the heterostructure conduction band. However, holes, ie, minority carriers generated in the n-type layer 13 by light conversion, which is one of the optical absorption processes, are not blocked at all. The detection device 1 operates as a photoconductor as follows.

Since the n-type layers 9 and 13 have a relatively high electron concentration and a high electron mobility, their resistance is negligibly small compared to the p-type layer 11. Any voltage applied externally to the detection device 1 appears through the p-type layer 11. The absence of a barrier to holes allows hole flow, but this flow is limited by the low availability of holes compared to the high concentrations provided by ohmic contacts. Since no electric field can be generated in the n-type layers 9 and 13, only a diffusion current flows. Ohmic contact 3 biased in the positive direction with respect to ohmic contact 5 (collector contact)
Detection device 1 equipped with (emitter contact)
Assume that the incident light enters from above. In this case, holes are generated in the n-type layer 13 and disappear by recombination at the ohmic contact 3, in the bulk of the n-type layer 13, or by transfer to the p-type layer 11. The width of the n-type layer 13 is the diffusion distance (~30μ
m), the bulk recombination process can be ignored, at least to a first approximation. It will be clear that since the concentration of optically generated holes is considerably higher than that of thermally generated holes, the latter concentration can also be neglected. The energy level diagram when biased in this way is shown in Figure 3a.
It was shown to.

When biased as described above, the generated carriers are swept away through the p-type layer 11. The hole is this p
It is the majority carrier of the shape layer 11 and has a longer bicycle recombination lifetime in this lightly p-doped material than the typical lifetime in n-type CMTs (1 to 20 microseconds). Strictly speaking,
A space charge control current flows into this region, but with an excessive electric field (1 volt per 10 μm, or 10 ³ V/cm) and a typical current (backland incident light at 300 K and f/2.5 field of view). It can be understood that if the electric field (corresponding to the luminous flux from) is flowing, the electric field will not change excessively. Therefore,
Solving the equation of continuity on the first plane provides a simple explanation of the flow of current. In the n-type layer 9, holes reach the forward biased interface by fractional carrier injection and accumulate until the rate of recombination due to the bulk process or in the ohmic contact 5 is balanced with the rate given by the current. be done.

The generation and distribution of minority carriers in n-type layer 13 is very similar to the situation in a reverse biased shallow junction photodiode. The optical incidence corresponding to the background state mentioned above is 6.8× for a thickness of 10 μm when the quantum efficiency is 0.9.
10 ²⁰ cm ^{-3- sec1} . In comparison, the degree of generation due to heat is ~5×10 ¹⁷ cm ^-3 sec ^-1 , or about 1/10 ³ . Therefore, the degree of generation due to heat can be ignored. The optically generated carriers diffuse to the ohmic contact 3, which can be characterized by a surface recombination rate Sc, or to the interface with the p-type layer 11, which appears as a surface with a recombination rate μE near the interface. or recombine within the bulk. Note that E represents the electric field within the p-type layer 11, and μ represents the mobility of holes.

If μ=300 cm ² /volt sec and E=10 ³ volt/cm then μE=3×10 ⁵ cm/sec. n-type layer 13 and p
The constant effective time for removal at the interface between the shaped layers 11 is 3×10 ⁻⁴ /μE=10 ⁻⁹ seconds, ignoring diffusion effects. This is limited by the diffusion time to reach the surface, approximately 3×10 ^-8 seconds, which is quite short compared to the bulk recombination lifetime.
When Sc≦3×10 ⁵ cm/sec, most of the carrier φ is transferred to the p-type layer 11. In this case, J= _φq , and the hole concentration p in the p-type layer 11 can be determined from J=qpμE. Under the conditions mentioned above, the current density is
If it is 0.1 A/cm ² , then p~1.1×10 ¹³ cm ^-3 . As a comparative example, the hole concentration of the non-depleted p-type layer 11 is ~
It is 1.3×10 ¹² cm ^-3 . At a high electric field in the p-type layer 11, these thermally generated carriers are reduced to a negligible extent with respect to the signal current.

In the n-type layer 9, the carrier concentration increases until the degree of recombination and the degree of supply are balanced. The effect of this structure is the distinction between the carrier generation region and the carrier recombination region.

When minority carriers are injected into the n-type layer 9, space charge reduction occurs. When the carrier concentration increases beyond thermal equilibrium, the electron concentration also increases to maintain an equilibrium state. Auger recombination predominates in this low bandgap material, which shortens the lifetime of minority gears. An opposite effect occurs in the n-type layer 13 due to the extraction field, but this is offset by the generation of excess holes by the incident light beam. In order to significantly reduce the recombination lifetime, the excess hole concentration must be brought to a thermal equilibrium electron concentration of ˜5×10 ¹⁴ cm ⁻³ depending on the doping.

Leakage current also occurs under zero irradiation. Under the conditions described above, this leakage current is ~3 x 10 ^-3 amperes/cm ²
, which corresponds to an RoA value of ~26 ohm ^cm2 . This high resistance value is due to the absence of fractional electron leakage. For a 50 μm square planar device, the saturation leakage current for an area of 2.5×10 ⁻⁵ cm ² is 7.5×10 ⁻⁸ Amps. In contrast, the background induced current is 2.5×10 ⁻⁶ amperes. (The leakage current is the standing current of a photoconductor that has the same focusing area but is excited in the longitudinal direction ~ 5×
10 ^-3 amps).

The noise of the detection device 1 is essentially background light fluctuation noise.

The capacitance of detection device 1 is extremely small, and in the case of a 50 μm square platen device ~
It is 0.02pF. Therefore, encapsulated structures result in capacitance being limited by the packaging and construction rather than by the underlying device characteristics.

Although the detection device 1 has many characteristics common to both photoconductors and photodiodes, it lacks some of the most significant drawbacks of these devices. The detection device 1 has zero output when the incident light illumination is zero, the tunneling seen in photodiodes is negligible, and there is no leakage current at zero signal as is commonly found in the best heterojunctions. Furthermore, the capacitance is extremely small and is about the same as a typical value of a pin diode structure, and the degree of space charge generation and recombination is also low. The detection device 1 can therefore be used in many diode circuits, even though the symmetrical structure described above requires biasing.

Thus, the aforementioned detection device 1 functions as a high impedance photoconductive infrared detector when the ohmic contact 5 of the collector contact is negatively biased with respect to the ohmic contact 3 of the emitter contact. Figure 3a].
The detection device 1 may also operate with contact AC or modulated AC bias. When using these operating modes, the detection device 1 operates as a nonlinear detector, ie a detector with a response that depends on the bias direction. During AC cycle, p-type layer 1
While the upper p-n junction between 1 and n-type layer 13 is reverse biased as in FIG. 3a, sensing device 1 operates as described above and photocurrent flows in the collector circuit. However, during another period during the AC cycle, i.e., the upper p-
While the n-junction is forward biased, the fractional carriers generated in the n-type layer 13 by irradiation are
It is attracted to the ohmic contact 3 as shown in Figure b. The output produced by the heterostructure device is therefore just a leakage current due to fractional carrier generation in the n-type layer 9. However, the number of optically generated fractional carriers in the n-type layer 9 is by no means large.
Infrared radiation in the 8-14 μm band is absorbed by the n-type layer 13 and only a very small amount, if any, can penetrate the detection device 1 and reach the n-type layer 9. Therefore, from the viewpoint of optical signals, the responsiveness rate is extremely high, and is mostly limited to photoconductive signals generated in the n-type layer 13 itself, but this is because the electric field within the n-type layer 13 can be ignored. It is so small that it can be ignored because almost no radiation penetrates beyond the n-type layer 13.

The detection device 1 can therefore be combined with an AC bias circuit. In this case, an effective optical signal can be extracted by arranging an integrating circuit following the Ohmic Tact 5. Since the detector device 1 is nonlinear in the irradiated state, the time-averaged AC signal generates a measurable organic component that depends on the intensity of the irradiation. However, in the absence of incident light, the current-voltage characteristic of the detection device 1 is excessively linear. In this way, integrating after applying an AC bias ensures that the output signal is zero when no beam is present.
Such a bias mode thus avoids any dark current problems. However, this dark current is in any case smaller than in conventional photoconductive detectors, since the detection device 1 is characterized by a very high impedance.

Instead of using an integrator in the AC biased circuit described above, a harmonic filter may be provided in the collector circuit. The detection device 1 is non-linear as described above and therefore generates measurable harmonics under illumination. An unmodulated AC bias may be used instead of a constant AC bias, in which case the resulting signal is demodulated to yield the desired signal. In this case the modulation waveform is selected such that the signal can be extracted at a frequency above the system 1/f noise knee frequency. Alternatively, the AC bias may be encoded and the output decomposed to remove noise.

The aforementioned detection device 1 consists of a three-layer structure 7 of CMT material, but the p-type layer 11 is made of another material,
For example, it may be formed of p-type cadmium telluride. In this way, when selecting a material other than CMT material, it is important that the material has wide band gap characteristics and that the material has a wide range of band gap characteristics between the p-type layer 11 and the n-type layer 13 and between the p-type layer 11 and the n-type layer 9. The objective is to cause almost no distortion of the value electron band through each of the -n-type interfaces. In the case of cadmium telluride, n-type
A low carrier concentration (compensated) p-type material with a Fermi level of the same or nearly the same depth above the valence band may be selected, such as n-type layer 9 and n-type layer 13 of the CMT coating. This p-type layer 11 of cadmium telluride is fixed by an acceptor-donor such as Fermi level Ag (Ea ~ 0.114 eV) or a combination of acceptors. When these CMT/CdTe materials are selected, the density of states in the valence band is similar, so the hole concentration is virtually constant throughout the three-layer structure 7. This setting of the Fermi level and the common anion law (this is
By applying CMT/CdTe common anion tellurium system), the valence band becomes horizontal,
There is no strain throughout the three-layer structure 7. Small distortions are reduced by novel changes in configuration.

Similar effects could be obtained with other systems that follow the common anion law. Gallium arsenide-gallium aluminum arsenide (GaAs-GaAlAs) and indium arsenide-idium gallium arsenide (InAs-InGaAs) systems are good examples.

A CMT/CdTe photodetector 21 is shown in FIG. 4 as a modified example. The photodetector 21 includes an elongated filament 23 which is a semiconductor layer made of an n-type cadmium mercury telluride material as an emitter region, and an intrinsic cadmium telluride material layer 2 on its upper and lower surfaces.
It is made of passivated material by attaching 5 and 27. One end of the filament 23 is provided with a read contact structure 29. The read contact structure 29 together with the filament 23 has a three-layer configuration similar to the previously described structure.

A p-type barrier region 31 is formed by converting a portion of the true cadmium telluride material layer 25 by dopant implantation or diffusion;
A collector region 33 of the same n-type CMT and a composite ohmic contact 35 are provided above the barrier region 31. The photodetector 21 may be an integrating focal plane photoconductive detector in an optically scanned system, such as the system described in GB 1488258.
It can be used as a photoconductive detector.
In such a system, the incident light passes through the filament 2
3 and scanned along the length of the filament 23 towards the read contact structure 29 at a speed compatible with the speed of movement of the bipolar photocarrier moving when a DC bias is applied to the filament 23. These bipolar carriers result from light conversion and their density increases according to their spatial relationship to the image. The fractional carrier component of the bipolar photocurrent is extracted at the readout contact structure 29. In this way, a read signal is generated, ie a signal associated with spatial changes in the light intensity of the scanned image.

It is also possible to use other materials for the collector region 33, for example made of a low gap p-type material (in this case resulting in a p ⁺ -p-n structure; see energy diagram FIG. 5b) or made of an organic material. It may consist of a microcontact (see energy diagram Figure 5a). For ohmic contacts, high work function metals are used. However, since such ohmic contacts are difficult to manufacture, the highly doped semiconductor of FIG. 5b is preferred.
This semiconductor is cadmium telluride, zero cap
It can also be formed by CMT or mercury telluride.

FIG. 6 shows another npn structure 41. FIG. This is a lateral device with n-type emitter and collector regions formed by depositing a single epitaxial layer on only one side of a substrate layer 43 of p-type wide bandgap material.
These areas are made up of photosensitive stripes 45 delineated by an etchant and the structures 4
Ohmic contacts 47 and 49 are provided at both end regions. Although the electric field distribution of the structure 41 is somewhat complicated, the principle of operation remains basically the same. The high electric field region exists only between the photosensitive stripes 45 of the n-type CMT. Substrate layer 43 is either self-supporting or more commonly attached to an insulating support substrate, such as the sapphire substrate 51 shown.
In either case, there is a large change in refractive index at the interface on the lower surface of this substrate layer 43. Therefore, the incident hole passing through the gap of the photosensitive stripe 45, which is the photosensitive n-type CMT layer, will be reflected, and most of it will be absorbed by the photosensitive stripe 45 after reflection. The physical dimensions of the photosensitive stripes 45 and the distance between the photosensitive stripes 45 must be kept small. This is because the bias electric field between the photosensitive stripes 45 takes a relatively long route.
The movement of the minority carriers within the photosensitive stripe 45 is essentially due to diffusion, so that the hole minority carriers do not emerge only from the corners of the photosensitive stripe 45.

A photodetector having the structure shown in FIG. 1 can also be easily modified for use as a "two-color" detector. In this case, the n-type layer 13 has a relatively wide bandgap.
That is, it is formed of a material having an intermediate band gap between the lower p-type layer 11 and the n-type layer 9. In order to clarify this application, a detector sensitive to incident light in the 3 to 5 μm band and the 8 to 14 μm band will be explained as an example. In this case, the n-type layer 13 is formed of an n-type CMT material suitable for detecting incident light in the 3-5 μm band (x = 0.28), and the n-type layer 9 is formed in the 8-14 μm band (x = 0.28).
It is made of n-type CMT material suitable for detecting incident light of 0.2). The Fermi level consists of two n-type layers 9 and 13
are graded within the p-type layer 11 to provide different levels. A small standing bias (equal to the work function difference) was then applied to obtain an equilibrium condition as shown in the energy diagram of FIG.
In the forward bias (drift from the surface to the inside, drift from left to right in FIG. 7), only 3-5 μm incident light is detected due to asymmetry. Incident light with energy less than this bandgap passes through the three-layer structure 7 and reaches the n-type layer 9 of low energy gap material. As a result, a photocarrier is generated, but in this bias direction, the electric field of the n-type layer 9 is so small as to be imperceptible, so that the sensitivity to incident light in the 8-14 μm band can be ignored. The signal in this case corresponds to absorption in the 3-5 μm band in the n-type layer 13. However, if the bias direction is reversed, 3~
The signal due to 5 μm band absorption becomes negligible. In this case, the photocarrier generated in the n-type layer 9 due to light conversion in the 8-14 μm band is the p-type layer 11.
The signal is generated by passing through a drift zone consisting of: The responsivity of the detector for incident light in the 3-5 μm band and in the 8-14 μm band is therefore DC
It can be switched by changing the direction of the bias. The detector may be AC biased, in which case the output of each band is selected according to phase. The signal is sensed by a gate amplifier.

A detector such as that shown in FIG. 1 can also be used as an up-converter. The upconverting effect occurs when the radiation efficiency of recombination within the collector is high. In this case, the bandgap of the collector is made wide enough so that the emitted incident light can be received directly or by a near-infrared vidicon camera.

Devices with inverted n-type and p-type materials are also possible, but such devices require greater control of the heterostructure interface. This heterostructural discontinuity in the band structure will be graded out as the layer grows, but due to this discontinuity there is an elongated zone with approximately intermediate carrier recombination properties. However, because of the high carrier mobility, the operating voltage of the device is not very limited. The interfacial area of the emitter can be very low and still provide the high drift velocity necessary to obtain high emitter efficiency. The minority carrier (electron) concentration within the emitter is extremely small. The doping concentration of p-type materials typically obtained is >1×10 ¹⁶ cm ^-3
Even if the lifetime is extremely short, if the diffusion coefficient is high, the diffusion distance will be several tens of microns as described above. However, if the occurrence of minority carriers is high, background military performance (BLIP) is difficult to achieve.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of an n-p-n type composite photodetector according to an embodiment of the present invention, FIG. 2, and FIG.
and b are band-level energy diagrams of the detector in Fig. 1 under zero bias, forward bias, and reverse bias, respectively, and Fig. 4 shows the structure of an n-p-n type composite photodetector as a strip detector. Cross-sectional views, Figures 5a and 5b are band level energy diagrams of the detector of Figure 1 with a metal collector and a degenerate semiconductor collector, respectively, and Figure 6 shows the structure of Figure 1. FIG. 7 is a cross-sectional view showing a modified two-layer structure photodetector, and FIG. 7 is an explanatory diagram showing band level energy of a two-color sensitive detector, which is a modification of the detector of FIG. DESCRIPTION OF SYMBOLS 1... Detection device, 3, 5... Ohmic contact, 11... P-type layer, 9, 13... N-type layer, 21... Photodetector, 23... Strip-shaped filament, 25, 27... Intrinsic CdTe material layer,
31... Barrier area, 33... Collector area, 3
5...Composite ohmic contact, 43...Substrate layer, 45...Photosensitive stripe.

Claims (1)

[Scope of Claims] 1. An n-type semiconductor emitter region made of a material sensitive to infrared rays, a collector region, and an emitter contact and a collector contact that are in contact with the emitter region and the collector region, respectively. The photoconductive infrared detector further includes a barrier region connecting the emitter region and the collector region, the barrier region including a p-type semiconductor material, and the barrier region including a p-type semiconductor material and a valence of the emitter material. It has a valence band that is almost common to the electron band, and has a wider band gap than the emitter material,
A heterojunction conduction band discontinuity is provided to the emitter region, and is adjusted so that it becomes a barrier to electron flow between the emitter region and the collector region, but hardly hinders hole flow. A photoconductive infrared detector. 2. The photoconductive infrared detector according to claim 1, wherein the emitter region and the collector region are arranged on opposite sides of the barrier region. 3. The emitter region is made of an infrared-sensitive semiconductor material having a strip shape and having two bias contacts, one of which is the emitter contact and the other is an additional contact, and between the two bias contacts, the said barrier region remote from the additional contact;
3. A photoconductive infrared detector according to claim 2, wherein the collector region and the collector contact combine to form a readout structure. 4. The photoconductive infrared detector according to claim 2, wherein the emitter region and the collector region contain the same semiconductor material. 5. The emitter region and the collector region include different bandgap materials of the same multicarrier type, one material sensitive to incident light in one wavelength band of the infrared spectrum and the other material sensitive to incident light in the other wavelength band. 3. The photoconductive infrared detector according to claim 2, wherein the photoconductive infrared detector is sensitive to incident light. 6. The infrared photoconductive detector of claim 1, wherein the emitter region and the collector region are adjacent to the same side of the barrier region. 7. A photoconductive infrared detector according to claim 6, wherein the emitter region and the collector region are formed from a single layer of material. 8. At least one intermediate region is included between the emitter region and the collector region, and the at least one intermediate region is arranged to relay holes from the emitter region to the collector region. A photoconductive infrared detector according to claim 6. 9. Claims 1 to 8, characterized in that the emitter region is one of ternary infrared sensitive alloys, namely cadmium mercury telluride, indium gallium arsenide or gallium aluminum arsenide. The infrared photoconductive detector according to any one of paragraphs. 10. The photoconductive infrared detector according to claim 9, wherein the barrier region also includes a ternary alloy material containing the same constituents as the material of the emitter region in different proportions. 11 said barrier region comprises a binary alloy material having a common anionic composition with the ternary alloy of said emitter region, said binary alloy material being either a cadmium telluride, indium arsenide or gallium arsenide alloy; A photoconductive infrared detector according to claim 9, characterized in that: 12. Any one of claims 1 to 11, characterized in that the materials of the emitter region and the barrier region are extrinsic and respectively n- and p-doped materials. The photoconductive infrared detector described in . 13. Light according to any one of claims 1 to 3 or 9 to 12, characterized in that the materials of the emitter region and the collector region are of the same multi-carrier type. Conductive infrared detector. 14. Any one of claims 1 to 3 or 9 to 12, wherein the collector region and the collector contact are formed from a single high work function metal layer. The photoconductive infrared detector described in . 15. Any one of claims 1-3 or 9-12, wherein the collector region comprises a highly doped semiconductor material of majority carrier type opposite to the emitter region material. 1
The photoconductive infrared detector described in . 16 A photoconductive infrared detector comprising an n-type semiconductor emitter region made of a material photosensitive to infrared rays, a collector region, and an emitter contact and a collector contact that are in contact with the emitter region and the collector region, respectively. wherein the detector further includes a barrier region connecting the emitter region and the collector region, the barrier region comprising a p-type semiconductor material and having a valence band substantially common to the valence band of the emitter material. It has a valence band,
It has a wider bandgap than the emitter material and provides a heterojunction conduction band discontinuity in the emitter region, providing a barrier to electron flow between the emitter region and the collector region, but substantially impeding hole flow. a photoconductive infrared detector, the emitter region and the collector region being arranged on opposite sides of the barrier region; An apparatus comprising: an alternating current voltage bias source connected between the ivy contact and the collector contact; and a signal current detector sensitive to the collector current generated by the photoconductive infrared detector. 17 A photoconductive infrared detector comprising an n-type semiconductor emitter region made of a material sensitive to infrared rays, a collector region, and an emitter contact and a collector contact that are in contact with the emitter region and the collector region, respectively. wherein the detector further includes a barrier region connecting the emitter region and the collector region, the barrier region comprising a p-type semiconductor material and having a valence band substantially common to the valence band of the emitter material. It has a valence band,
It has a wider bandgap than the emitter material and provides a heterojunction conduction band discontinuity in the emitter region, providing a barrier to electron flow between the emitter region and the collector region, but substantially impeding hole flow. the emitter region and the collector region are arranged on opposite sides of the barrier region, and the emitter region and the collector region are arranged in different bandgap materials of the same multiple carrier type. a photoconductive infrared detector, characterized in that one material is sensitive to incident light in one wavelength band of the infrared spectrum and the other material is sensitive to incident light in the other wavelength band. a voltage source connected between the emitter contact and the collector contact, a switch for changing the polarity of the voltage source, and a signal sensitive to the collector current generated by the photoconductive infrared detector. A current detector. 18 A photoconductive infrared detector comprising an n-type semiconductor emitter region made of a material sensitive to infrared rays, a collector region, and an emitter contact and a collector contact that are in contact with the emitter region and the collector region, respectively. wherein the detector further includes a barrier region connecting the emitter region and the collector region, the barrier region comprising a p-type semiconductor material and having a valence band substantially common to the valence band of the emitter material. It has a valence band,
It has a wider bandgap than the emitter material and provides a heterojunction conduction band discontinuity in the emitter region, providing a barrier to electron flow between the emitter region and the collector region, but substantially impeding hole flow. the emitter region and the collector region are arranged on opposite sides of the barrier region, and the emitter region and the collector region are arranged in different bandgap materials of the same multiple carrier type. a photoconductive infrared detector, characterized in that one material is sensitive to incident light in one wavelength band of the infrared spectrum and the other material is sensitive to incident light in the other wavelength band. an alternating current voltage bias source connected between the emitter contact and the collector contact, and a phase sensing for separating signals generated during positive and negative half cycles of the alternating current bias, respectively. A device comprising: a detector.